Australasian Plant Conservation

Monitoring the effects of fire on the Button Wrinklewort (Rutidosis leptorrhynchoides)

Catherine Ross and Amy Macris
Fenner School of Envrionment and Society, Australian National University, Canberra. Email: u4524334@anu.edu.au

The endangered Rutidosis leptorrhynchoides in flower.
Photo: M. Fagg

Introduction

The Button Wrinklewort (Rutidosis leptorrhynchoides) is a perennial forb native to Themeda triandra grasslands and grassy woodlands in south eastern Australia. Since European settlement, loss of habitat and overgrazing have contributed to a decline in the population; the species is now listed as endangered and is limited to a number of small populations in the ACT and western Victoria (Scarlett & Parsons, 1990). There is some evidence to suggest that fire could be an important tool in Button Wrinklewort conservation. Many of the remnant populations are found in areas which are frequently burnt (such as railway reserves), and in areas where this burning has ceased, populations have suffered declines (Scarlett & Parsons, 1990). Further, research has shown large gaps between grass swards to be of critical importance for Button Wrinklewort recruitment and survival, and fire has been recommended as a way of maintaining these gaps (Morgan, 1997). However, there are concerns that burning may damage Button Wrinklewort plants and encourage weed growth, and current management guidelines recommend that remaining populations should be protected from fire (ACT Government, 1998). In this study we monitored the effects of an autumn burn on a large population of Button Wrinkleworts in order to improve knowledge of the direct and indirect relationships and inform management practices.

Methods

The study was carried out in Stirling Park, Yarralumla, ACT, where the National Capital Authority (NCA) intended to undertake prescribed burns as part of their fire hazard management plan. In order to measure the effect of fire, a transect method was used to estimate percentage cover of Button Wrinkleworts and covariates (including St John’s Wort, Chilean Needle Grass, Plantain and other weeds, native grass, bare ground, litter and shade) before and after the fire. The change in percentage cover at each transect was averaged across the burned plots (n=12) and compared with control plots in an adjacent area (n=12).

Transects were 5 metres in length, marked with fire proof stakes and placed in areas where there was at least one Button Wrinklewort present. Percentage cover was estimated by recording the species or covariates (mentioned above) present at 10 cm intervals along the transect (presence was recorded if any part of the plant intersected a vertical line perpendicular to the tape measure at that point).

Pre-burn data were collected in April 2011. Post-burn data were collected in September 2011, following the control burn carried out by the NCA in May. The same transect method was used to quantify the fire intensity immediately after burning. At 10 cm intervals along the transects the intensity was classified as either not burnt (no evidence of burning), lightly burnt (some leaf litter remaining) or heavily burnt (all/most leaf litter reduced to ash).

Mean change in percentage cover by treatment. While there was no difference in the change in Button Wrinklewort cover between treatments, significant differences were found for bare ground, native grass and total weed cover. In all cases, the heavily burnt plots were significantly different from the lightly burnt and control plots which did not differ significantly from each other.

Results

Analysis of the baseline data collected before the burn showed that the treatment and control transects were comparable, with almost identical Button Wrinklewort distributions and few significant differences in mean densities of other covariates (Student’s t-test). Cover of St John’s Wort, Plantain and total weeds were negatively correlated with cover of Button Wrinklewort (REML correlation).

The fire intensity was extremely variable and patchy; five of the twelve transects were more than 90% unburnt. As a result, in the analysis the treatment transects were further classified as ‘lightly burnt’ (<10% burnt, n=5) and ‘heavily burnt’ (>10% burnt, n=7).

The change in percentage cover was compared between treatment and control plots. There was a slight but non-significant trend for Button Wrinklewort cover to decrease in both the control and treatment plots. The trend was stronger in the heavily burnt plots but still was not significantly different from the control.

The seven heavily burnt plots experienced a significant increase in bare ground (+23%) when compared with the lightly burnt and control plots. While native grass cover decreased in all treatments there was a significantly greater decrease in the burnt plots (-20%) and there was no difference between the control and lightly burnt plots. Finally, there was a significant decrease in Plantain (-13%), Chilean Needle Grass (-3%) and total weed cover (-19%) in the heavily burnt plots, compared to the control plots.

Discussion

Contrary to the concern that fire may cause mortality in adult Button Wrinklewort plants, there was no evidence of mortality as a result of the fire treatment. Following the fire, Button Wrinkleworts were observed to regenerate from basal buds despite complete removal of all above-ground material, even in the most heavily burnt patches. This indicates that the Button Wrinklewort is able to tolerate quite an intense burn without significant losses.

The Button Wrinklewort is an inter-tussock forb, and usually grows in areas where the grass does not form a dense canopy (Scarlett & Parsons, 1990). A study by Morgan (1997) found that the Button Wrinklewort is highly gap-sensitive, with seedling emergence and survival as well as growth rate and flower production dependent on gaps greater than 30cm wide. While the present study did not look specifically at the size of inter-tussock gaps, the observed increase in bare ground and decrease in native grass cover following fire treatment may create gaps that increase germination and survival in the following year.

Studies have shown that unburnt or grazed sites tend to have a greater proportion of exotic species than regularly burnt areas (Stuwe & Parsons, 1977; Morgan & Lunt 1999). The present study found that the fire treatment resulted in a significant decrease in total weed cover in heavily burnt plots (-19%) while the controls experienced an increase of more than 8%. Herbaceous exotics such as Plantain compete with the Button Wrinklewort to occupy the same inter-tussock spaces, while Chilean Needle Grass forms dense swards that exclude inter-tussock species. Both species are considered to be particularly problematic in Stirling Park and this reduction in cover is likely to be beneficial for the Button Wrinklewort and other native species.

Conclusion

Within the short time-frame of this study, the fire treatment had no direct effect on Button Wrinklewort abundance. However, it did affect covariates such as bare ground, weeds and native grass cover that may indirectly benefit the Button Wrinklewort in the longer term by reducing competition and forming gaps that are important for germination and survival.

We recommend that fire be considered as a management strategy in Button Wrinklewort populations along with current management practices, and that further monitoring of these sites as well as additional burning trials should be carried out to assess the long-term effects including flower and seed production, recruitment, and recurrence of competitors.

Acknowledgements

We would like to acknowledge our supervisor Chris McElhinney. Also thanks to James Pittock and Phil Gibbons for their expertise and assistance with the experimental design.

Morgan, J.W. and Lunt, I.D. (1999) Effects of time-since-fire on the tussock dynamics of a dominant grass (Themeda triandra) in a temperate Australian grassland. Biological Conservation 88(3): 379-386.